Films of zinc oxide and related compounds [ZnO, ZnO(OH)5, Zn(OH)Cl9] are electrodeposited cathodically in aqueous zinc chloride solutions using dissolved oxygen as a precursor. The influence of the precursor concentrations, pH, and deposition temperature on the growth, composition, and properties of the films are investigated by means of in situ techniques: voltammetry electrochemical quartz-crystal microgravimetr surface pH, and ex situ techniques: X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy. The deposition mechanism is analyzed in terms of electrochemically induced surface precipitation due to an increase of local pH resulting from the oxygen reduction reaction. This approach allows us to explain the formation of either zinc hydroxychloride compounds or zinc oxide from their calculated solubility diagrams. In conditions of the formation of ZnO, a dramatic effect of temperature is observed, with a transition between amorphous insulating zinc oxyhydroxide to well-crystallized and conducting zinc oxide when the temperature increases (Ttran,jtjon 50 °C).

Communications ADVANCED MATERIALSConsequently, the initial precipitation of Ti and A1 or Ni and A1 in segregated phases, followed by an exothermic reactive-sintering process between the Ti and A1 or Ni and A1 nanocomponents produced the sintered microstructures. Crystallite growth was restricted to nanometer dimensions because diffusion distances for the reaction were short and reaction temperatures were only transiently high.In summary, we report the first general chemical synthesis of nanocrystalline aluminide intermetallics. The method uses readily available starting materials, a simple solutionbased processing technique, and low applied temperatures. The small crystallite sizes and sintered microstructures result directly from the chemical pathway followed and the participation of a nanoscale reactive-sintering event. In a separate study,t211 we have induced Ni and A1 to react and precipitate in the same amorphous phase in the solutionphase step, which precludes a subsequent reactive sintering and results in a non-sintered nanocrystalline microstructure. Consequently, grain size and microstructure are amenable to chemical control. We will report the results of these experiments and the mechanical properties of densified nanocrystalline aluminide compacts in the near future.

Electrodeposition of inorganic compound thin films in the presence of certain organic molecules results in self‐assembly of various hybrid thin films with new properties. Examples of new discoveries by the authors are reviewed, taking cathodic formation of a ZnO/dye hybrid as the leading example. Hybridization of eosinY leads to the formation of highly oriented porous crystalline ZnO as the consequence of dye loading. The hybrid formation is a highly complicated process involving complex chemistry of many molecular and ionic constituents. However, electrochemical analyses of the relevant phenomena indicate the possibility of reaching a comprehensive understanding of the mechanism, giving us the chance to further develop them into industrial technologies. The porous crystals are ideal for photoelectrodes in dye‐sensitized solar cells. As the process also permits the use of non‐heat‐resistant substrates, the technology can be applied for the development of colorful and light‐weight plastic solar cells.

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The mechanism of chemical bath deposition of cadmium sulfide thin films from the ammonia‐thiourea system is studied in situ by means of quartz crystal microbalance technique (QCM). The influence of reaction parameters (concentration of reactants, pH, anions, temperature, stirring rate) is determined. The growth is thermally activated with an activation energy of about 85 kJ/mol, which probably corresponds to a chemical step related to the decomposition of thiourea. The results are well interpreted by assuming an atom‐by‐atom growth mechanism. A model is presented, which fits most of the experimental results quantitatively. It involves two or three rate‐limiting surface steps, the formation of normalCdS taking place via a surface complex between thiourea and cadmium hydroxide. Analytical expressions are given, allowing prediction of the rate under various conditions in this system.

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